Ronald Acuna Jr. suffered a complete tear of his left ACL in the first inning of Sunday's game against the Pirates and is expected to undergo surgical reconstruction in the near future.
The injury occurred when Acuna, after taking a leadoff of second base as he prepared to steal third, had to get back quickly and his left knee appeared to buckle in classic noncontact ACL injury fashion. He rolled on the ground in pain initially but was able to eventually walk off the field, escorted by members of the Braves' medical staff.
Interestingly, Acuna told reporters Sunday (before it was announced that he had torn his ACL and would miss the season) that the injury felt less severe than when he tore his right ACL in 2021. "Don't feel that painful, any pop or anything," he said. "... Don't think it's that bad."
Ronald Acuña Jr. exits the game due to a non-contact injury on the bases. pic.twitter.com/RHZCJ9ldBe
— Bally Sports: Braves (@BravesOnBally) May 26, 2024
While an audible pop is often associated with a complete ligament tear -- and given Acuna's comments, appears to be what he experienced with his first ACL injury -- it is not universal, particularly if the ligament already has some laxity present. Acuna did miss approximately a month in his rookie year (2018) with a mild left ACL sprain and a left knee contusion, an injury that could have predisposed him to eventual ACL failure in that knee when subjected to the right amount of stress.
So what can be expected for the future of the reigning National League MVP who has now suffered his second season-ending knee injury in three years?
Acuna's injury can't be fully appreciated until after he undergoes surgery (specifically whether this is an isolated ACL tear or whether there is any additional structural damage to the knee), at which point a rehabilitation timeline will emerge. No matter what the details are, there is little to draw from when it comes to comps as ACL injuries are relatively rare in baseball.
How long will Acuna miss?
In a study published in 2022 looking at the epidemiology of lower extremity injuries in the baseball athlete, the authors found complete ACL tears to be uncommon among minor and major league baseball players, accounting for just 2% of all knee injuries. When they do occur, however, they are responsible for the most missed time of all knee injuries, resulting in an average absence of 156.2 days. If it is in fact an isolated ACL tear and the surgery is straightforward, there's reason to be optimistic that Acuna could return in time to start the 2025 season.
Will Acuna be the same hitter when he returns?
Despite a lengthy recovery period, there is a very high rate of return to play for baseball players of all levels following ACL reconstruction. One study published in 2015 (Fabricant, et al) focused on return to play rates of major league position players. Although the sample size was small given the relative infrequency of the injury, 88% of players were able to return to at least 30 major league games. Perhaps more noteworthy was the finding that players with a rear batting leg injury saw a decline in batting average of 12.3% but players with a front batting leg injury saw an increase in batting average of 6.4%.
Acuna's injury in 2021 was to his right leg which, as a right-handed hitter, was his rear batting leg. And he had some struggles when he initially returned in 2022 as he worked to rediscover his power and his timing. His batting average declined in his first post-op year (.266 in 2022 from .283 in 2021) but, as is often the case, he was much improved the following season, one year removed from surgery -- to the tune of 41 home runs and 106 RBIs, not to mention a career peak batting average (.337). Given that Acuna has already proven he could exceed pre-injury performance levels following his first ACL surgery and that this latest ACL tear is to his lead batting leg, it would seem there is less reason to be concerned about his productivity now.
Will the injury rob Acuna of his stolen base prowess?
It turns out there is no association between the side of injury and stolen base metrics. Theoretically, Acuna's skill set should not be threatened, but it is worth remembering that there is a limited sample size to draw from when it comes to comparisons. Acuna dwarfed his own stolen base numbers last year when he swiped 73 bags; he might have been hard pressed to duplicate that effort even when fully healthy. He also sustained this latest injury while attempting a steal. Returning to play following ACL reconstruction often challenges a player's confidence, especially when performing the same maneuver that resulted in the injury. On the one hand, Acuna has his prior successful return to play experience from which he can draw confidence; on the other hand, his first injury occurred while fielding, not baserunning.
At the very least, familiarity with the injury, the surgery and the ups and downs of rehab sets Acuna up for success, as does his youth. Acuna, who will be just 27 years old when the 2025 season gets underway, has a chance to do something else rarely seen in his sport; his return would make him one of the exceedingly few major league baseball players to return from two ACL injuries (one to each knee) sustained during his professional career, with Wilson Ramos being the lone recent example to which we can point.
(Editor's Note: The final sentence has been update to specify ACL injuries to both knees. Royce Lewis is a recent example of a player who returned after suffering two ACL injuries as a pro, but that was both to the same knee.)